Automatic manual transmissions (commonly called “AMT”) are increasingly widespread: they are structurally similar to a traditional manual transmission except that the clutch pedal and the gear selector lever operated by the user are replaced by corresponding electric or hydraulic servo-controls.
An automatic manual transmission is provided with a transmission control unit which drives the servo-controls associated with clutch and gearbox during a gear shifting or during a drive-away; moreover, during a gear shifting or during a drive-away, the transmission control unit communicates with an engine control unit for making an appropriate adjustment of the engine torque delivered by the engine so as to adjust the engine operation according to the change in gear ratio and avoid a temporary undesired increase/decrease of the engine rpm when the clutch is open or however in opening or closure. Such a control mode applies both to a traditional single-clutch gearbox and a twin-clutch gearbox; the only difference between the two gearbox types is that during a gear shifting in a single-clutch gearbox there is also a central time slot in which the clutch is fully open (i.e., the engine idles with no load) while in a twin-clutch gearbox the two clutches cross and therefore there is a situation of opening/closure of the clutch throughout the gear shifting.
In a design phase, an engine model is determined which allows to predict the engine behaviour and therefore allows to determine how to control the engine in order to get the generation of a desired engine torque. Moreover, in a design phase, a transmission model is determined which requires the knowledge of the function of clutch transmissibility, which provides the torque which is transmitted by the clutch according to the degree of opening (i.e., the position in case of a position control in a dry clutch or the hydraulic pressure in case of a pressure control in a clutch in oil bath) of the clutch itself.
In the known automatic manual transmissions currently marketed, during the gear shifting or during the drive-away, the transmission control unit determines a target torque which must be transmitted by means of the clutch and a target rotation speed of the drive shaft according to the desired evolution of the gear shifting or the drive-away; in other words, the desired evolution of the gear shifting or the drive-away is described by a target speed and a target longitudinal acceleration, and such target speed and longitudinal acceleration may determine a target torque which must be transmitted by means of the clutch and a target rotation speed of the drive shaft.
By knowing the target torque which must be transmitted by means of the clutch as a start up, the transmission control unit uses the transmissibility function of the clutch for determining how to control the clutch actuator so as to pursue such target torque. Moreover, the transmission control unit communicates to the engine control unit a target torque which must be generated by the engine according to the target torque which must be transmitted by means of the clutch; the engine control unit uses the engine model for determining how to control the engine so as to pursue the target torque which must be generated by the engine.
However, both the transmissibility function of the clutch and the engine model are relatively inaccurate; specifically, both models are affected by the errors due to aging of the components, the errors due to the dispersion of the characteristics of the components, and the inevitable errors inherent in the model. Moreover, many external factors may affect the transmission of the torque by means of the clutch, and especially the generation of the engine torque, more or less randomly and unpredictably.
Because of the inaccuracies in the transmissibility function of the clutch and the engine model, the control of the torque may be inaccurate and therefore more or less significant offsets may occur between the torque actually generated by the engine and the torque actually transmitted by the clutch; such offsets determine undesired variations (temporary increases or decreases) of the engine rotation speed which are particularly bothersome as they are clearly felt by the driver (and by possible passengers) both acoustically when hearing the noise generated by the engine and physically as they may cause discontinuities (i.e., pulse variations) in the longitudinal acceleration of the vehicle. Consequently, the undesired variations in the engine rotation speed transmit to the driver (and the possible passengers) the feeling that the automatic manual transmission does not operate properly or however efficiently.
The above-described undesired variations in the engine rotation speed during a gear shifting or during a drive-away may be mitigated by means of a feedback control on the engine rotation speed; in other words, a PID controller is used which modifies the torque generated by the engine to try and remove a speed mistake, i.e., an offset between the actual engine rotation speed and the desired engine rotation speed. However, the PID controller is not able to completely remove undesired variations in the engine rotation speed, specifically when the variations are significant. Moreover, the PID controller may introduce oscillations in the engine rotation speed (which tends to oscillate around the desired value) and may introduce delays which degrade the overall dynamics of the control of the gearshift or the drive-away.
The undesired variations of the engine rotation speed during a gear shifting or during the drive-away are very mitigated and therefore less noticeable in small-medium capacity (i.e., power) engines having a fairly high mechanical inertia, but are very amplified and therefore very evident in high-performance sport engines which have a high capacity (i.e., power) combined with a very low mechanical inertia. Consequently, the need for minimizing as much as possible the undesired variations in the engine rotation speed during a gear shifting or during a drive-away is considerably felt in the high-performance sport engines, while it is less important in the small-medium capacity engines.
FR2854848A1 describes an adaptive control device for coupling an engine to a gearbox in a vehicle. The control device comprises a module for monitoring and transmission, a module for controlling the torque of a clutch, and a module for controlling a clutch actuator; the module for controlling the clutch actuator comprises correcting means which determine a signal for controlling the actuator which allows the variation between a nominal value and a measure of a physical quantity for controlling the clutch, and adjusting means for adjusting parameters of the correcting means in accordance with quantities of the physical environment and in accordance with the current actuator behaviour.
Overview
Examples described here provide a control method of a vehicle provided with an automatic manual transmission during a gear shifting or during a drive-away, which control method is free from the above-described drawbacks and is simultaneously both easy and cost-effective to be implemented.
According to some examples, there is provided a control method of a vehicle provided with an automatic manual transmission during a gear shifting or during a second drive-away as claimed in the attached claims.